The present invention relates to the field of communications, and, more particularly, to antennas and wireless terminals incorporating the same.
Recently, the size of wireless terminals has been decreasing. Many contemporary wireless terminals are less than 11 centimeters in length. Thus, there is increasing interest in small antennas that can be utilized as internally mounted antennas for wireless terminals. Inverted-F antennas, for example, may be well suited for use within the confines of wireless terminals, particularly wireless terminals undergoing miniaturization. Typically, conventional inverted-F antennas include a conductive element that is maintained in a spaced apart relationship with a ground plane. Exemplary inverted-F antennas are described in U.S. Pat. Nos. 5,684,492 and 5,434,579, which are incorporated herein by reference in their entirety.
Furthermore, it may be desirable for a wireless terminal to operate within multiple frequency bands in order to utilize more than one communications system. For example, Global System for Mobile communication (GSM) is a digital mobile telephone system that typically operates at a low frequency band, such as between 880 MHz and 960 MHz. Digital Communications System (DCS) is a digital mobile telephone system that typically operates at high frequency bands, such as between 1710 MHz and 1880 MHz. The frequency bands allocated for mobile terminals in North America include 824-894 MHz for Advanced Mobile Phone Service (AMPS) and 1850-1990 MHz for Personal Communication Services (PCS). Accordingly, internal antennas are being provided for operation within multiple frequency bands.
Conventional approaches for providing multiple frequency bands utilize band switching. These approaches focus on switching in the antenna matching network or in the active portions of the antenna, i.e. the feed points of the antenna. The active portion of the antenna is typically a high current point, thus, losses in the switching devices may be considerable. Furthermore, antenna matching networks are often bandwidth limited.
Embodiments of the present invention provide antennas for communications devices and wireless terminals. A conductive element is provided along with a ground assembly including a ground element coupled to the conductive element. The ground element has a first state and a second state. The first state provides a first resonant frequency band when the ground element is in a first relative position that is a first distance from the conductive element. The second state provides a second frequency band when the ground element is in a second relative position that is a second distance, different from the first distance, from the conductive element.
In some embodiments of the present invention the ground element includes a first ground plane in the first relative position spaced apart from the conductive element and a second ground plane, distinct from the first ground plane, in the second relative position spaced apart from the conductive element. In the first state the first ground plane may be coupled to the conductive element and the second ground plane may not coupled to the conductive element and the first and second ground planes may both coupled to the conductive element in the second state. Alternatively, in the first state the first ground plane may be coupled to the conductive element and in the second state the second ground plane may not coupled to the conductive element and the second ground plane may be coupled to the conductive element and the first ground plane may not coupled to the conductive element.
In further embodiments of the present invention, a controller may be configured to select a system frequency band within at least one of the first resonant frequency band and/or the second resonant frequency band and to generate a system frequency band identifier signal based on the selected system frequency band. Alternatively, a user interface may receive a user input designating at least one of the first resonant frequency band and the second resonant frequency band. The ground assembly may further include a switch configured to couple at least one of the first ground plane and/or second ground plane to the conductive element responsive to the system frequency identifier signal and/or the user input. The switch may further be configured to decouple at least one of the first ground plane and/or second ground plane from the conductive element responsive to the system frequency identifier signal and/or the user input. The switch may include at least one of a MEMS switch, a PIN diode switch, an electronic switch and/or a mechanical switch.
In still further embodiments of the present invention, the ground element may include a single ground plane. The ground plane may be in the first relative position in the first state and the second relative position in the second state.
In some embodiments of the present invention, a controller configured to select a system frequency band within at least one of the first resonant frequency band and/or the second resonant frequency band and generate a system frequency band identifier signal based on the selected system frequency band. Alternatively, a user interface may receive a user input designating at least one of the first resonant frequency band and the second resonant frequency band. The ground assembly may further include a motion means for moving at least one of the ground plane and/or the conductive element responsive to the system frequency band identifier signal and/or the user input.
In further embodiments of the present invention, the first resonant frequency band may include at least one of 800 MHz, 900 MHz, 1800 MHz and/or 1900 MHz. The second resonant frequency band may include at least one different one of 800 MHz, 900 MHz, 1800 MHz and/or 1900 MHz. The conductive element may be a planar inverted-F antenna (PIFA) element.